DEBATE -- TAPE OR DISC?
video recorders and camcorders use tape or disc? The future is being mapped out
as we speak, and itís not as clear cut as you might think...
the future of home video recording is in a state of flux, though this time the
debate is not so much to do with which tape format weíll all be using in ten
years time, but which disc system. Thatís right, it looks as though tape has
had its day, the next generation of video recorder could well use re-recordable
optical discs, and needless to say there are at least two rival formats so once
again the race is on to see which system will prevail.
about digital video tape, wasnít that supposed to be the replacement for VHS as
a home video recording system? Well, yes it was, and still could be, but things
have moved on at an unexpectedly fast pace and now disc technology has
leapfrogged developments in tape; some industry pundits now predict that digital
video cassette (DVC) systems will have a role in camcorders, rather than VCRs,
for a while at least, until suitable miniature disc recording systems have
look at the main protagonists, and how the various systems work it might be a
good idea to try and clear up some of the confusion surrounding the multitude
of optical disc systems and recording formats that are coming on to the market.
All of them are descended from, and look pretty much like the familiar 5-inch
(120mm) audio CD which first appeared in 1981. From that has evolved a large and
growing family of CD-like optical discs, though the information that they
contain, and the way in which they are used varies enormously. Currently there
are at least twenty variants on the CD theme, the most common ones, and the
oneís youíre most likely to have come across include CDi, CD-ROM, Photo CD and
Video CD. Incidentally, you may have read about red, yellow orange, white etc.
Ďbookí standards for each system, that refers to the colour of the covers of
the detailed specification for each format, and quite frankly neednít bother us
too much at this stage.
The way all
CD type discs work is exactly the same; digital information is stored on the
disc and is represented by a zillions of microscopic mirrors or Ďpitsí. A
tightly focused laser bean scans across the surface of the spinning disc,
reflections from the surface bounce back into a photo-sensitive cell, and the
signals from it are converted into the appropriate medium. So, on an audio CD,
for example, the digital data is converted into an analogue form, fed into an
amplifier and speakers, so we hear it as sound. On a CD-ROM or CDi disc the
information is computer software, that can be directly processed by a personal
computer or video games console. Some CDi discs and Video CD contain a mixture
of computer software and compressed digital video data -- movies and TV
programmes -- plus digital stereo soundtracks, that can be viewed on a TV, using
a suitable player, Photo CDs contain digital data that is used to store
high-quality still photographs and images.
as far as it goes but it means that we, the consumer, need to have lots of separate
boxes, a CD player for music, a cassette deck if we want to make our own audio
recordings, a VCR to record TV programs and watch movies, and if weíre really
fussy about quality, a laser disc player as well. Now, the argument goes,
wouldnít it be wonderful if we could have everything in one box, using just one
standardised recording and playback system. Well, thatís the way it looks like
going The next generation of discs has arrived, under the general heading of
CD-R, where the R stands for recordable. Basically there are two types of CD-R
disc. The first ones can be recorded, but not erased, theyíre called WORM or
write-once-read-many times discs and theyíre the type used for Photo CD
applications, where information can be written to the disc in a number of
sessions, but once the disc is full up,
thatís it. The second type is a re-useable disc, which is a bit like magnetic
tape in that the information can be written and erased as many times as you
like. Most manufacturers are aiming for one-million read-write cycles, which
should be enough to satisfy most users.
CDs have opened a giant can of worms, if youíll excuse the pun, because it makes
copying discs so simple, and because information is stored in a digital form, every
copy or clone should be as good as the original. The concern is all about the potential
for large-scale piracy, not just for audio CDs but for computer software as
well; in some discs can be worth several hundred pounds. The solution has been
to put data onto blank discs, so players and decks recognise them and only
permit them to be used for specified purposes, and to devise an anti-piracy
system called SCMS (Serial Copy Management System) which prevents more than
once copy of a copyright disc being made.
us more or less up to date. The problem with the standard CD is the maximum
capacity is limited to around 600 megabytes of data, which equates to 45
minutes of audio or just a few minutes of sound and video. The actual amount of
video varies as itís possible to compress the data by various clever means.
Most of them rely on the fact that one frame of video is almost exactly the
same as the ones before and after it, so it makes sense to process only on the
bits that change, i.e. movement. Depending on the level of compression itís
possible to squeeze an hour or so of tolerable-looking video onto a CD, but
thereís a limit to how much compression can be used before the picture starts
to look really horrible. The bottom line is that thereís simply not enough
capacity on a normal CD for a full length feature film.
nutshell thatís the key to commercial success to establishing CD as a
mass-market medium for video as well as audio, that and the prospect of
re-recordable discs. Video discs have had a chequered history and to date the
only survivor of the eighties disc format war -- Laser Vision -- has been only partially
successful; the main problem is that itís a playback only system, and everyone
acknowledges that the 12-inch disc is not very convenient, moreover they are
expensive to make, and because the information is recorded in an analogue form,
thereís the added difficulty of differing TV standards, a problem that neednít
arise when vision signals are encoded as digital data. Discs can be the same,
for every market, standards conversion can be carried out by the player, thatís
the theory at least...
number of ways around the problem of getting a movie onto a single disc, the
most obvious one is to increase the amount of data it can hold by increasing
the number of reflective pits. That can be done by reducing the gap between
adjacent tracks, and the size of data pits themselves. The only thing wrong
with that is the wavelength of the laser beam, which effectively dictates how
small the pits can be. The solution is to use a laser with a shorter
wavelength, and thatís more or less what has happened. In fact the holy grail
of CD is the blue laser, which has the shortest wavelength of all, they exist
now in prototype form but in the meantime lasers with shorter wavelengths are
in production and now almost the entire consumer electronics industry is
working feverishly to develop high-capacity disc systems. So, format skirmishes
aside problem solved? Well, not quite, thereís still the question of being able
to record on a disc, not just once, but a limitless number of times.
successful attempt to develop a re-recordable disc for consumer/domestic
applications came from Sony with their magneto-optical (MO) Mini Disc. Large MO
discs have already been developed for video applications but thereís a couple
of problems, the main one being backwards compatibility with existing CD media.
For any domestic system to succeed home decks must have backwards compatibility
and be able to play existing audio CDs, as preferably one or two other members
of the CD family as well, like CDi, and Photo CD. At the moment thereís simply
too many technical and political problems for that to happen with MO
technology. The search has been on for another recordable disc technology and
the most promising one so far seems to be the phase-change system.
been doing a lot of the pioneering work on this technology and their phase
change discs utilise a chemical compound, sandwiched between the outer
transparent layers of the disc. The compound can exist in two states, a
normally amorphous condition, where the molecules are randomly scattered, and a
crystalline state, where it becomes highly reflective. The trick has been to
develop such a compound, and devise ways to make it change back and forth
between the two states. The most successful system so far uses a powerful laser
that momentarily heats tiny sections of the compound to 600 degrees centigrade,
it cools and crystallises in a minute fraction of a second, creating the
necessary pattern of reflective pits. The compound can be changed back to its
amorphous -- i.e. non-reflective state
-- by re-heating it to 170 degrees with a lower intensity blast of laser energy.
Now all of
the various elements are in place, including the inevitable formats battle. The
first shots were fired by Philips and Sony earlier this year, who have jointly
developed HD-CD (high-density CD). It has a capacity of 3.7 gigabytes, thatís
enough for 137 minutes of compressed video. Shortly afterwards Toshiba
announced their double-sided SD (Super Density) disc system, which has a capacity
of 5 gigabytes per side, thatís a possible 180 minutes per side. On that basis
the SD system looks like a winner, (though someone is still going to have to
figure out where to put the label ...) but the clincher has been the fact that
it is backed by a powerful group of consumer electronics companies, including
Matsushita (Panasonic and JVCís parent company), Pioneer, Thomson and Hitachi,
and, equally importantly, their associated software companies, which include
Hollywood majors MCA and Time-Warner.
The die is
cast and our guess is the timetable will go something like this. In the next
few months the first consumer CD-R machines will appear in the shops. These
will be able to replay and record audio CDs, prices will initially be around
£500 to £750, but should quickly fall to £200 or so, TDK who have just launched
the first consumer CD-R disc reckon the price of blank discs will cost between
£10 to £15. No-one wants another ruinous formats battle in the high-street, hopefully
good sense will prevail and one of the two high capacity systems will become
established as an international standard within the next year or so, our money
is on Toshibaís SD system. If things progress reasonably smoothly after that then
we could see hardware in the shops in three to five years, which ironically is
about the same time-scale as the digital video cassette system.
choice between tape and disc recorders with equal performance capabilities we
suspect disc will win easily, though past experience has shown that the
technology is only part of the equation. The main determining factor has always
been the availability of and variety of software. Here too disc-based systems
have the advantage. Blanks discs are cheaper than tape and pre-recorded software
on disc can be produced quickly and cheaply, many times cheaper in fact than
pre-recorded tapes. The format has a number of other advantages, namely discs
do not wear out, they have shorter -- almost instantaneous --access time, and
they take up less storage space.
nothing in this business is certain and there are any number of flies in this
particular ointment, not least the prospect of doing away with pre-recorded
software altogether with video-on-demand systems, a huge increase in the number
of satellite channels and the not inconceivable prospect of any emergent system
getting a big thumbs-down from the buying public. Whatever the outcome, though,
the next five years should prove very interesting indeed.
” R. Maybury 1995 0603